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%I #13 Aug 30 2020 18:02:36
%S 0,1,3,6,9,15,20,27,34,43
%N Minimum number of painted cells in an n X n grid to avoid unpainted tetrominoes.
%e For n = 4, painting only 5 cells would leave an unpainted tetromino, but painting the following 6 cells avoids all unpainted tetrominoes:
%e . . X .
%e X X . X
%e . . X .
%e . X . .
%Y Cf. A337501.
%K nonn,more
%O 1,3
%A _Rob Pratt_, Aug 29 2020
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